This invention relates generally to the measuring torque transmitted through shafts such as engine crankshafts and the drive shafts in generators and other such applications, and more particularly to detecting transmission of torque by sensors involving use of magnetostrictive material positioned on the surface of such shafts.
Torque sensors of the aforementioned type are generally well known in the art as disclosed for example in U.S. Pat. Nos. 4,631,796, 4,823,617, 4,765,192 and 4,823,620 to Inomata et al., Hase et al., Hase et al., and Edo et al., respectively. The shaft mounted magnetostrictive means utilized in such torque sensors is in the form of elongated strips or ribbons having a generally planar cross-sectional geometry and made of an amorphous magnetic alloy material, the compositions of which are disclosed, for example, in U.S. Pat. No. 4,763,030 to Clark et al. The magnetostrictive strips are also annealed to remove mechanical strains according to the disclosures in the Inomata et al. and Clark et al. patents.
The referred to prior art torque sensors, as disclosed by way of example in the aforementioned Hase et al. and Edo et al. patents, are formed from magnetostrictive amorphous material wound on the shaft to be measured for torque within two complementary coil sections having helix angles of 45 degrees. Stationary pick-up coils disposed in inductive relation to such magnetostrictive coil sections will respectively detect torque applied to the shaft in either direction in order to measure torque in both directions. In order to obtain accurate measurement of torque, the helically wound, magnetostrictive material must be fixed to the surface of the shaft. Toward that end, such material was bonded by use of suitable adhesives on the cylindrical surface of the shaft or within grooves formed in the shaft according to the aforementioned Hase et al. and Edo et al. patents, for example.
The aforementioned prior art torque sensors were believed to have high figures of merit because of the good transduction properties of the magnetostrictive material based on the use of transverse field annealed amorphous magnetic alloy compositions and establishment of its fixed relationship to the shaft by bonding thereto of generally planar strips or ribbons of such material. However, the bonding of such magnetostrictive strips or ribbons to the external cylindrical surface of the shaft or within grooves formed therein by use of bonding adhesive has created non-homogeneous strains sharply reducing the figure of merit. The application of the magnetostrictive material to the shaft surface by sputtering to avoid the latter problem has been found to be very difficult. Accordingly, the potential of amorphous magnetic alloy materials in providing large values of figure of merit and low hysteresis for torque sensors as aforementioned, has not been satisfactorily exploited.
It is therefore an important object of the present invention to enable full exploitation of the aforementioned properties of amorphous magnetic alloy material for magnetostrictive types of torque sensors so as to avoid use of shaft mounted electronics or moving contacts found to be generally unsatisfactory.